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In color flash photography a phenomenon know as red eye can occur. The term "red eye" refers to a person's photographically reproduced pupil(s) when they appear red instead of their normal black coloration. [This effect also occurs in flash photography of animals, although the characteristic color may not be red.] The reddish colored light is the result of the light produced by the flash reflecting off the eye's layer immediately behind the retina. To prevent this problem two procedures have been used during image capture: (1) increase the ambient light levels or (2) separate the flash from the camera by several inches. The first solution reduces the size of the pupil thus reducing the quantity of light reflected and also lessens the amount of required flash illumination. The second measure prevents the lens from detecting the reflected light since it is confined to a narrow beam directed back towards its source--the flash. Unfortunately the amateur photographer is not always in a position to execute either of the above solutions. In general the amateur uses a flash to account for the location's lack of ambient light. In addition, many point-and-shoot cameras, as well as some SLR's, have the flash located closely to the lens.
After the image has been digitally captured it is possible to correct the eye color defects. Commonly assigned U.S. Pat. No. 5,130,789 issued Jul. 14, 1992 entitled "Localized Image Recoloring Using Ellipsoid Boundary Function" to Dobbs et al, describes a method by which a region's chroma and luma channels are modified after an operator identifies a region surrounding an eye.